1. Field of the Invention
The present invention relates to the field of electrical therapy for treating pain and other conditions, in particular to electro-acupuncture and percutaneous electrical nerve stimulation therapy. The present invention is more specifically directed to a method and device capable of delivering continuous pain relief through percutaneous electrical nerve stimulation both in and out of clinic.
2. Prior Art
Electrical therapy has long been used in medicine to treat pain and other conditions. One of the forms of electrical therapy is Transcutaneous Electrical Nerve Stimulation (TENS). The TENS method is based on a hypothesis of Melzack and Wall from 1965. They proposed that activity in coarse, afferent nerve fibers (A-beta-fibers that convey pressure, touch, and vibration) inhibits impulse transmission in pain pathways at spinal cord level. The coarse nerve fibers have a low threshold for electrical stimulation and are therefore simple to activate by stimulation using electrodes placed on the skin. Usually stimulation frequencies of 2–120 Hz are used for conventional TENS. Electro-acupuncture is another example of electrical therapy, which has been used successfully for a number of years. Current U.S. patent application Ser. No. 10/068,826 submitted by the same applicant on Feb. 11, 2002 describes an improved electro-acupuncture device.
In recent years, Percutaneous Electrical Nerve Stimulation (PENS) has been used and investigated for the management of acute and chronic pain syndromes. PENS is a new analgesic therapy that combines advantages of both electro-acupuncture and TENS. PENS therapy utilizes acupuncture-like electrodes placed in the soft tissues to stimulate peripheral sensory nerves at the dermatomal level corresponding to a local pathology. TENS, on the other hand, is a procedure that involves electrical stimulation on the surface of the skin through cutaneous electrode pads. Electro-acupuncture is similar to PENS except that it is influenced by acupuncture theory of the meridians, energy channels, and their distribution for a choice of sites to be stimulated with electricity. In modern medical acupuncture stimulation sites are chosen from both meridian and neurological considerations. A difference between PENS and TENS electro-acupuncture from the physiological perspective is well described in the American Journal of Pain Management Vol. 12 No. 4 by Ong and Ho. The article shows differences and similarities in mechanisms of pain interruption between TENS and acupuncture/electro-acupuncture along the ascending nociceptive pathways, namely, at peripheral, spinal segmental, supraspinal, and cortical levels. On peripheral level electro-acupuncture stimulates mainly the pinprick Adelta and small type III fibers for its effect. TENS stimulates mainly the tactile Abeta and large type I fibers for its effect. On the spinal level electro-acupuncture's effect is mediated via the inhibitory enkephalinergic stalked cells in lamina II of the spinal grey matter. TENS's effect is mediated via interneurons with GABA receptors in the spinal cord and this stimulates the inhibitory neurons. On the supraspinal level electro-acupuncture activates pituitary mechanisms releasing enkephalins and produces analgesia throughout the body. Conventional TENS are mostly segmental not involving pituitary mechanisms, and the analgesic effect is only segmental.
In clinic both electro-acupuncture and PENS seem to be significantly more effective than TENS. Ghoname and colleagues conducted a randomized, controlled, crossover study to compare effectiveness of PENS, TENS, and exercise therapy in 60 patients with chronic low back pain secondary to degenerative disc disease. The authors described the PENS as a therapy that combines the advantages of TENS and those of electro-acupuncture. Compared with sham PENS, TENS and exercise therapy, PENS was more effective in improving function, pain, physical activity, and quality of sleep. PENS therapy was preferred by 91% of the patients.
PENS therapy has been found to be effective in the management of pain associated with a number of conditions, including acute herpes zoster (Ahmed, Craig, White, Ghoname et al., 1998), the prevention and treatment of migraine headaches after electroconvulsive therapy, cancer pain secondary to bone metastases (Ahmed, Craig, White, & Huber, 1998). Compared with dorsal column stimulation, the PENS technique is less invasive, less costly, and less risk ridden. Electro-acupuncture has been also found effective for many conditions including, but not limited to, Irritable Bowel Syndrome and dysmenorrhea.
Currently, a PENS procedure is performed in clinic by a pain specialist, typically, by physiatrist, anesthesiologist, or acupuncturist. Patient is usually prone on the treatment table, when two or more needles/electrodes are inserted in the back and around the spine according to the location of pain. Electrodes are kept in place for 30 min to 1 hour, while being stimulated with alternating electrical current generator at frequencies typically from several to 100 Hz. Since the electrical resistance of the skin is short-circuited by the inserted electrodes, and the actual electrical current through the electrodes is very small (in milli-amperes range), the electrical stimulator can operate for a long time from a single 9V battery. These electrical devices are currently available as electro-acupuncture machines. They offer variable frequencies, intensities, and one or multiple outputs. Needle electrodes are inserted perpendicular to the skin at variable depths, depending on the area, patient's anatomy, and the etiology of pain, anywhere from several millimeters to several centimeters. Electrical clips with electrical wires are attached to the electrodes before the electrical stimulator is turned on. An example of the improved electrodes can be found in aforementioned U.S. patent application Ser. No. 10/068,826 filed by one of the s of the present application on Feb. 11, 2002. There have been many attempts to improve the electrodes and to find ideal stimulating modes (frequencies and intensities) for PENS in prior arts. Examples can be found in U.S. Pat. No. 6,549,810 issued to Paul Leonard et al. in 2003 and U.S. Pat. No. 6,701,190 issued to Brad Gliner in 2004.
While there are some differences in electrode design, duration of the procedure, and frequency modes between PENS procedures, several characteristics have remained the same in all prior arts. Namely, electrodes/needles are inserted perpendicular to the body and the external parts of the electrodes protrude above the skin. The patient has to be stationary on the table during the duration of the procedure, for 30 to 60 minutes. Also, treatment can be only repeated during patient's next visit to a pain clinic.
In order to overcome the aforementioned disadvantages of the prior art, the applicant developed a principally novel method and a device for percutaneous electrical nerve stimulation and electro-acupuncture. The new method and device are disclosed in pending U.S. patent application Ser. No. 10/962,299 filed by the same applicant and are based on inserting the needles/electrodes into the prescribed acupuncture/trigger points at slant angles so that the external parts of the needles/electrodes can be secured against the skin of the patient. The new method and device allow the use of different types of percutaneous electrodes and angular or perpendicular insertions, as long as the external parts of electrodes are in flush with the patient's skin. An angular insertion of the needles/electrodes, however, has significant advantages over perpendicular insertion in case of PENS. First, the inclined position of the needle provides distribution of current over a larger area of the patient's tissues for the same depth of insertion since the inserted part of the needle is longer in the inclined position than in the perpendicular position. Second, as the projecting part of the needle is secured to the surface of the skin, a patient is not restrained by the needles and may have freedom of motion. In other words, after insertion of the needles the patient may leave the clinic and may not be bound to the clinic during subsequent usage of the device.
However, experience showed that patients experience some discomfort. Furthermore, the known device exhibits some difficulty in use and precision control of the procedure because it is impossible to change a position of the inserted electrode in the body without compromising needle's sterility or without removing the whole electrical assembly. This is because the needle/electrode is kept in flash with the skin under an adhesive electrode. Furthermore, when a needle is used as an electrode, it should be bent after insertion so that the axis of insertion does not coincide with the axis of the needle in the inserted state. Therefore, the deformed needle tends to straighten out and to overcome the bending force, and special measures, such as an adhesive pad are needed for retaining the exposed part of the needle in a bent state and in contact with the patient's skin. When a patient that carries needles with the projecting portions held in contact with the skin by adhesive pads moves, these movements may disconnect the adhesive pads so that the projecting ends of the needles will straighten out and become unrestricted for movements. This may loosen the part of the needle inserted into the skin and even lead to extraction of the needle from the skin because of friction contact of the needle handle with the patient's clothes.